In many power electronic circuits, the current oscillates or commutates from one semiconductor device to another equivalent semiconductor device via a commutation loop. By way of example, two-level converters comprise two semiconductor switches which are connected to a capacitor and thus with the capacitor form a commutation loop. In general, the commutation loop has a certain leakage inductance produced, for example, by the conductors that connect the semiconductor components and by the inductance of the capacitor.
If a commutation of the current occurs between the two switches, the current does not fall abruptly owing to the leakage inductance, but rather is temporally dependent, which leads to voltage spikes that load the semiconductor switches. Since each semiconductor switch can also block only a limited voltage at its inputs, a high leakage inductance also reduces the performance or switching speed of the two-level converter.
By way of example, a capacitor having a low inductance, such as a film capacitor, for instance, can be chosen in order to reduce the leakage impedance. Moreover, connections having a low inductance, such as, for instance, planar busbars, twisted lines, etc., can be used between the capacitor and the semiconductor switches.
It is also possible to arrange a snubber capacitor (damping capacitor) spatially near the semiconductor switches, which can reduce the size of the commutation loop and thus reduce the leakage inductance.
Power semiconductor switches, which are generally embodied in a planar fashion, are arranged for example together with cooling elements in a stack and can be connected to form a so-called presspack. The presspack or stack can also comprise the snubber capacitor which can be arranged laterally on the presspack or stack.